U.S. Pat. No. Re. 30,643, issued on Jan. 9, 1981 to E. Nill et al., describes a method of aluminizing the inside of the panel of a television picture tube. A lacquer film is deposited over the phosphor materials of the screen, to provide a smooth surface on which an aluminum layer is condensed. Because both the film and the aluminum layer cover not only the phosphors but also the smooth lateral surfaces of the panel, the portion of the lacquer on the sidewall is roughened prior to aluminum deposition so that gas, released during the volatilization of the organic materials in the screen and film, can escape through small openings in the aluminum layer, thereby preventing blistering of the layer. To roughen the lateral surface, boric acid is sprayed on the lacquer film. The method described in U.S. Pat. No. Re. 30,643 has the drawback that boric acid does not promote sufficient adhesion between the aluminum layer and the glass surface of the lateral portion of the panel. Consequently, even if blistering of the aluminum layer does not occur during panel bake, flaking of the aluminum layer may still occur, thereby generating undesirable conductive particles within the tube. An additional drawback is that if any of the boric acid is oversprayed onto the phosphor screen, the boron in the boric acid reduces the efficiency of the ZnS:Ag blue phosphor, resulting in a dark or yellow appearance of the affected phosphor.
U.S. Pat. No. 3,582,389, issued on Jun. 1, 1971 to T. A. Saulnier, Jr., discloses an aqueous filming emulsion of acrylate copolymers including at least one of four possible additives. The additives may include colloidal silica and a soluble silicate. The panel containing the phosphor screen is heated to about 40.degree. to 46.degree. C. immediately prior to filming. The purpose of the colloidal silica and the soluble silicate in the filming emulsion is to reduce peeling of the metal layer from the bare glass areas of the panel after the bake-out step. In making films with emulsions which have a minimum film-forming temperature above room temperature, sufficient heat must be applied to the panel to cause the film to dry rapidly in order to accumulate emulsion solids over the phosphor area. However, the inclusion of colloidal silica in the filming emulsion does not completely eliminate the formation of blisters in the aluminum layer overlying the blend radius, i.e., the smooth, sharply curved portion of the panel, and the sidewall.
U.S. Pat. No. 4,990,366, issued to A. Pezzulo et al. on Feb. 5, 1991, discloses a solution applied over the dried filming emulsion, to the blend radius and to the sidewall, to promote adhesion and prevent blistering of the subsequently deposited aluminum layer. The solution contains 1 to 3 percent, by weight, of a constituent such as oxalic acid, or ammonium oxalate, or a colloidal silica, or boric acid. Because the screen is heated to a temperature above the minimum film-forming temperature when the filming emulsion is applied, the panel temperature, after the emulsion deposition step, is typically still above the minimum film forming temperature (e.g., about 35.degree. C.) when the adhesion-promoting, blister-preventing solution is applied. If the panel temperature drops below 35.degree. C., the panel must be reheated to above the minimum film-forming temperature before the solution is sprayed thereon, to promote rapid drying of the solution. A drawback of this process is that manufacturing time is increased and the filming apparatus must have additional stations to permit reheating of the panel for the application of the solution.
A need therefore exists for a post-filming process that provides an adhesion-promoting, blister-preventing material on at least the blend radius and sidewall of the panel while maintaining the efficiency of the screen-making process.